Day of Days - S1-E2
Revealing mistake: When placing the German grenade into the barrel of the German, gun you can see the cord used to set timer is still attached. (00:36:40)
Suggested correction: The cord doesn't have to be fully removed for it to work so showing it like that is not a mistake. The grenade will smoke quite a bit if the primer is ignited so even if the cord isn't fully removed they'll know quickly enough the pull was hard enough to ignite it.
Day of Days - S1-E2
Character mistake: Winter calls his officer Major Strayers, when actually Strayers was a Lt Colonel. Winters made the same mistake in Currahee when walking upstairs with Capt Sobel.
Suggested correction: Strayer didn't become a Lt. Colonel until 1945. In fact, Winters took over leading 2nd battalion of the 506th from Major Strayer when he became a Major and Strayer was promoted to lead the regiment.