I can't see the photo either ....but if they're labeled as 2 3/4" - then 2 3/4" is the fired length of the hull / not the overall length when they're crimped.
I'm not really surprised that there is a little difference in the unfired lengths of some different brands of shells / but you might have a 3" shell in there / that got mixed in too - so double check them !
The overall fired length of a shell / has little or nothing to do with what kind of shot size is in the shell / or how many ounces of shot is in the shell...
Be careful on box labels ....there isn't a "standard" for the industry ...and sometimes people misread Dram Equivalent "DR Eq" as length ... Dr Eq is an approximation of the velocity of the shell ...and 2 3/4 is a common Dr Eq...
Just make sure the fired length of a hull - does not exceed the length of the chamber on your gun and you're ok.