I am not new to knitting but I’m not very good. I have a pattern which says:
Back: knit in pattern to 25cm and then shape armholes
Left Front: knit in pattern to 27cm and then shape armholes
Right Front: knit in pattern to 27cm and then shape armholes
I am not sure if this would mean that the fronts would not match the back correctly?
Thank you
This does sound a bit unusual, but there could be a reason in the overall design. For example, I have seen shoulder seams set towards the back of a garment as a design feature.
What pattern are you using?
Hmm, I can’t see any reason for the difference. If anything, it seems you would want to be matching up the stitch pattern “stripes” at the sides.
Maybe one of the more experienced folks can chime in, like @salmonmac, @Creations, @engblom.
(And I just realised that set-back shoulder seams wouldn’t account for a different length below the armholes, so please ignore that thought.)
Thank you for your replies. I remain confused but will keep thinking 
Welcome to the forum!
The only reason I can think of for the different back and fronts lengths is a variation of a split hem with the back shorter than the fronts. Usually with a split hem the back is longer than the fronts.
You might read further in the pattern, maybe under Finishing to see if the difference is accounted for or look at a schematic if there is one. Otherwise, you could just go with the same length to the armholes. The back and fronts will match even if you miss a design feature.
I’m definitely not experienced, I just talk a lot!
Is there a striped cardy pattern with this too? Have you checked the instruction on that one to see if it also says to mpwork a different length?
I would definitely want the striped eyelet pattern to line up if I made this so I’d do front and back the same length unless I could find a good reason in the pattern not to.
