In response to my points about the danger of having to add more increases to the sleeve, that it might make the sleeve too long, a commenter asks a reasonable question:
'With a few calculations, though, surely you could just knit the number of rows that would give you the correct length for the size you actually want?'Absolutely, of course you can adjust the length of the sleeve. It's not that hard, relatively speaking, and knitters who are comfortable with the math do this all the time!
But my point was this: knitters often believe (hope?) that they can just work another size and have it magically work out, with no math at all. And as my example illustrates, and your question supports, this just isn't true.
Another reader has asked for some more basic guidance on checking gauge and counting - I'll post on this in the next day or two. Any other questions I can answer?