Ithaca help needed

Can anyone out there shed some light on approximately when Ithaca made the following changes?
MSH, from checkered to ribbed
Hammer from T1 checkered to T2 serrated
slide stop from checkered to serrated
The only references I can find indicate these changes occured sometime in / around 1943.
If anyone has some info/serial number ranges, I certainly appreciate any ifo you have. Also, serial # 14586xx shows a 1943 manufacture, but on CoolGunSite, this # shows having shipped 6/3/44. Wondered if that would make the "late" parts more likely.
Thanks for any/all help.
John

Hi John, I rely on coolgunsite for info. 1943 production shows "checkered" as the norm for 1943, or at least, most of '43. The only tidbit of info I can provide is that my 862xxx was shipped April 28, 1943. So an ending sn for 1943 would be...? Hopefully the experts will weigh in, ie approx monthly production during the year. I ASSume that all checkered parts were used up before the newer serrated parts were dipped into. Regards, Ray