I needed to replace the forks on my 1988 XR250 but was having a hard time sourcing the forks. So I started looking for other compatible options. It was difficult for me to figure out this information. So I will leave this here for the world.
For reference on the changes in fork years, according to a forum post
3 versions of 84+ XR250R forks: - 84-85 have 38mm stanchion tubes - All 86-04 have 41mm tubes - 96-04 have early version of cartridge forks and have clicker adjusters.
For reference on compatbility of 86+ forks, according to a forum post
I put 03 xr 250 forks on a 87 xr 250. It all bolted up with no mods. Used the 87 wheel brakes,clamps,axle.