Claims not sources. Of course it'll be different, what I disagree with is the response as a simple slider from Entente<--------->Central Powers and the lack of an Entente response. The broad strokes was still against the Central Powers, now let's look at the details.
Where did you get 8 billion from, the amount at the end of the war that they paid off steadily over a hundred years in 2015? Long-term loans were much easier to service being essentially on British credit and spread out over decades. The short-term loans was 1.4 billion over the period and the actual challenge. Looking into it, I'd agree with you, they floated a 500million loan in 1916 through JP Morgan and withdrew another 400million in unsecured loans; which Wilson put a pause on because he thought he can force a settlement. This is well within his power, plays to his personal glory-seeking impulses, and avoids his habit of ignoring congress. This is of course the same Wilson that declared war a year later in response to unrestricted submarine warfare (USW).
For one, its hard to see how the US stays neutral with USW and Americans die by the week; without getting into a POD replacing the Wilson administration the same pressures are there for war and its up to Germany to scale back on USW. There would be less economic and material pressure from few ships sunk; a requirement for American-belligerency instead of war.
"economic orthodoxy was that its international standing was linked to its gold reserves, which were set to run out in early 1917; technically, Great Britain was facing bankruptcy"
Strachan, Hew: Financing the First World War, Oxford 2004, pp. 59-60.
Yet as we know today and as the British found out, value isn't about gold but confidence. The Central Powers would love it that their major concern was the lack of bullion, a matter of confidence as opposed to real material deficits causing inflation and starvation. Given the choice between losing and inflation they will inflate away and as the Germans, Russians and Austrians show they can get a good 2-3 years out of inflation. They knew this will come with hard, possibly permanent damage to British financial domination post-war but it is depth they can use. Much like the central powers should they choose, they can prioritize military nitrates instead of fertilizer; slaughter breeding flocks; cut back on pesticides just like the Central powers did three years earlier with similar effects down the road in 1919-1920; they'd start to starve by then yet the Germans would be long-gone.
Exports was a factor; one the Entente didn't like but should Wilson play hardball with loans they can do it by dialing back offensives and war production. The Central powers in contrast would love the ability to export surpluses and trade, yet they're just stuck with the imbalances.
"The Treasury did not know how many American dollar securities were held in Britain. Obtaining them raised uncomfortable questions for a liberal state at war. Initially the Treasury borrowed securities from holders on a volunteer basis. It was not until 1917 that American dollar securities were sequestrated. Over the life of the scheme, 1915-19, the American Dollar Securities Committee bought or borrowed bonds and shares worth $1,423 million."
Wormell, The Management of the National Debt 2000, p. 180.
Understandable as a democracy with rule of law and a financial center, Britain really didn't want to confiscate American assets from its citizens, yet it was an option and can cover a majority of the 1.4 billion short-term loans.
At the same time, they can sell valuable real-estate like Bermuda or the Caribbean islands, it'd be a hit to imperial prestige; but no where as much of a hit as losing the Great War.
Source: Broadberry and Harrison (2005: 7-10).
Let's subtract Russia, which is soon to be out with its at around 700-800$ per capita and 91 million; and you'd end up with 168 million French and Brits at around 530 billion: the imperial cores alone were still twice the size of the Central Powers economies. It also comes with some hidden advantages; higher personal incomes allow for greater taxation before they hit the impoverishing bottom like Germany. Higher personal income from efficiency and mechanization also means more men to mobilize.
There is plenty Britain alone can tap into, so let's say they economize. This isn't the days of just in time shipping, supply shocks take time to propagate and stockpiles can be relied upon short-term it'd take months-a year to show and respond to. As this happens in April lots of things changes.
1. They can cut back on Romanian shipments, Romania stays out. Germany and AH goes hungrier without Romanian loot, its going to be a cold and hungry winter.
2. Would they still go with the Neville offensive knowing supply shocks a year from now? Probably yes, but it also means longer time to build-up for the next action probably in early 1919. If not then they tone it down, after all one of the basics of siege warfare is starvation and time isn't on the German-side; the defensive such a future shortage causes will be better for French causalities on the defensive. This isn't 1918 where the Entente figured out how to do proper mechanized pushes.
2.5 Should the disasters Neville offensive continue yeah morale will plummet, might be more than IOTL; unknown to the Central Powers wo are busy in the east. The French will need to recoup and be incapable of offensives for at-least a year; so what? Just like IOTL not willing to die attacking is a far cry from letting Germans advance, the French being democratic and capable of learning will put someone like Petain to restore morale. Not that the Germans can do much in the west with 127 German Divisions facing off 106 French, 56 British, and 6 Belgian divisions of similar quality.
3. Russia folds: while the Entente rushes supplies from Feb-Oct, the drain soon stops with the peace-making Bolsheviks.
4. Less men and material are sent to the Salonika front; not that the Bulgarians can do much against mountains anyways; yes they'd last a bit longer not that this imports a single calorie into Bulgaria.
5. They cut back on non-essentials: Britain was 40 % of American trade and it traded more than just war material; they can cut back and prioritize war materials at the expense of farming and consumer goods.
Once again I find it odd that the Entente, faced with different situations (whether finances or material) won't adapt by cutting back on consumption or offensives. That from a position of strength with more men, material, and control of trade can't just sit back on the defensive against an adversary that's deficient in food and material.
Read the TL in progress earlier in the thread if you want details on the food situation.