"newer P220's"
Not sure exactly how "new" to which we are referring. My understanding was that "newer" P220's all have milled slides, and take solid, knurled, one piece breechblock pins like the rest of the "newer" milled slide P series. To the best of my knowledge, there are no "new" stamped P220 slides. If SIG is still selling replacement 2 piece roll pins, they are no doubt for (all) the older stamped slide pistols.
The trigger return springs are easily told apart. The older pattern were crescent/half moon shaped. The newer pattern are more L-shaped, and have a circular center portion. I do not believe they are interchangeable but could be mistaken. I would definitely be replacing a trigger return spring on any older SIG P series, ESPECIALLY a heel mag release version, as that indicates an early model for sure.
BTW, the solid, one piece pins for the milled slides DID come in different diameters, and the knurl patterns were a bit different too. SIG apparently changed the hole diameters in the slides of the milled pistols by just a wee bit. You could beat and beat on one but not get it to seat if it was the wrong type. I had to keep both pin sizes in stock, and noted which pistol (by serial number) took which pin (old or new style) in my log book.