Are you not able to do both 25 and 10 man for raids? I seem to be only able to do one or the other and not both back to back.
It depends on which expansion the raid was released in, but for most raids that had 10 man & 25 man versions once you’ve done one you won’t be able to do the other until the next reset.
https://us.forums.blizzard.com/en/wow/t/can-i-clear-the-same-raid-twice-on-the-same-lockout/734804/3
Unfortunately in Cata, blizzard made it so that 10 man and 25 mans shared a lockout since they made it that 10 and 25 mans dropped the same ilvl loot (in order to prevent 25 man guilds from double dipping loot). This affected Wrath raid as well, which have different loot (and ilvls) for 10 / 25 modes.
So yeah, you can only pick one. Which is a pain for ICC since you have 4 modes to get Tmogs from (10N, 10H, 25N, 25H). At least though some items share appearances for 10H and 25N. Such as paladins lookalikes.