2004 Vanilla RLC, had it PUSHed some time ago then dropped the travel to 100mm a year or so ago.
now trying to set the travel back to 125mm, put the 2 spacers above the spring but the fork won’t extend further than 110mm-ish. so that’s a bit weird.

anyone know what the problem might be?

Have you removed all spacers from the plunger shaft assembly below the main spring? I imagine you have, otherwise you’d really struggle to get the two spacers in above the spring and get the top cap back on.

Should look like this:

confused. I thought the travel adjustment was determined by the number of spacers above the main spring (as per the assembly in the middle of your photo).

How do I get to the spacers at the bottom of the plunger assembly?

The spacer(s) on the plunger shaft are what dictates how much the fork extends. You need to undo the spring side foot nut on the lower and gently tap the shaft and slide it out through the top of the stanchion.
Quite straight forward really.

Detailed instructions here:

http://www.enduroforkseals.com/id28.html

ok ta. The Fox manual seems to miss that bit out.
Makes sense though. CHeers.