Back again...
I read the FAQ and it was quite clear:
I quote:
"Q: This realistic U-boat availability stuff sounds good, but I want my new U-boat now! What can I do?
A: U-boat availability in the stock SH3 applies equally to all Flotillas even though some Flotillas often received a U-boat type months after the type was available to other Flotillas. In addition, the stock SH3 really got it wrong with the 1st Flotilla!
SH3 Commander corrects these anomolies by providing availability dates that reflect the real dates experienced by each individual Flotilla.
...
So, want to revert back to the stock SH3 U-boat availability dates? Simply edit or delete 'U-boat availability.cfg', located in your SH3 Commander\Cfg folder.
...
quote end.
I did delete that file. But...
I searched the file structure in /program files/sh3 commander.../roster and found a file concerning XXIs: It's SSTypeXXI.cfg. I opened it and:
"[UnitClass]
ClassName=SSTypeXXI
UnitType=200
AppearanceDate=
19440627
DisappearanceDate=19450621
DisplayName=Type XXI
[Unit 1]
Name=U-2501
DOC=19440627
DOD=1945050
Does this affect the availability date? It says June 1944, not April...
Or does it have to do only with the individual u-boat numbers?