Wrong numbers.
704 typ VII u-boats were commmissioned overall.
only 141 were commissioned in 1941.
(of a grand total - all classes considered - of 188 u-boot that year).
Your "744" seems thus to be the overall total for VIIs, not the 1941 total.
http://www.uboataces.com/uboat-type-vii.shtml
Your right. Missread my own source.