I'm going to have to disagree with you Dr. Waterhouse, the Earldom of Warwick followed the same rules of succession like other titles at the time. It was just that at the time of The Wars of the Roses, things regarding the Earldom's succession had gotten pretty...interesting.
First let's go all the way back to mid 1200s and 7th Earl of Warwick, both of them. The holder of the Earldom from 1242-1253 was Margaret du Beaumont who inherited from her brother, Thomas the 6th Earl. When she first inherited the title she was married to John Marshal who by jure uxoris became 7th Earl of Warwick, but he died the same year she inherited the title. Margaret and John didn't have any issue, however the title didn't go to any of John's brothers because it wasn't his to pass on. Margaret married John du Plessis in 1247 a favorite of Henry III who made him 7th Earl because of this marriage, they had no issue when she died in 1253. John du Plessis lived until 1263, but the last 10 years of his life he wasn't Earl of Warwick. Margaret was succeeded by her distant cousin, William Maudit who became the 8th Earl.
Now lets go to the 15th and 16th Countesses of Warwick. The 15th Countess of Warwick was the toddler Anne de Beauchamp, who succeeded at around 3 and died at around 6. Now because off the inheritance laws around there was serious question of how the estates would be split up, if at all. The 16th Countess of Warwick was another Anne de Beauchamp, married to Richard Neville son of Richard Neville jure uxoris Earl of Salisbury thus the monikers Warwick (son) and Salisbury (father) to distinguish the two. Warwick the Kingmaker was able to keep most of the estates intact, but lost a few pieces to Edmund Beaufort making him join York's side in the future. Warwick the Kingmaker only was called to Parliament and became influential because of his wife, who couldn't be called to Parliament thus being called the jure uxoris 16th Earl of Warwick.
When Warwick died in OTL, because he had no son and two daughters. Edward IV, George, and Richard basically just started dividing and fighting amongst themselves over everything Warwick had once had. All the estates connected to the titles of Salisbury and Warwick, Edward IV took into his possession even while Anne was alive (a sonless widow at that point was screwed). The titles of Salisbury and Warwick went to George via Isabel, again even though Anne was still alive. George and Richard battled over the Beauchamp and Despenser inheritances that Anne had received and her husband had used. What happened to Anne? Her sons-in-law sent her off to some out of the way place and didn't bat an eye.
If Richard Neville and Anne de Beachamp had had a son along with their OTL daughters, then that son would be in-line for the Earldom of Warwick (and all the estates connected to it however those could be "in custody" of Edward IV leaving only the aforementioned Beauchamp and Despenser inheritances for said son) once Anne died, unless he died before her or was attained by joining future rebellions against the Yorkists. Basically any attainder against The Kingmaker would only affect the Earldom of Salisbury because he was only Earl of Warwick by right of his wife who actually held the title.