Very true. Standard sizes not only changed over time, but come in local flavours. Which only goes to show that one needs to spend some time measuring up an old building.

..4in X 4in joist...

Funny thing is, that you can say 2×4 (to-tom-fire) here and people will understand that you mean a two-thumbs-[by]-four[-thumbs] construction material. I keep doing it myself, but it is silly. Not only have we been metric since 1887, but the local inch (tomme=thumb) was 26,1 mm - not the English 25,4 mm. So as you say, no wonder the odd wall is a bit off-angle... ok