After having my new LF wide angle lens separated from its Linhof board, I now wonder about the front and rear lens spacing. (See my earlier post here; that post mentions it's a technika board but it was in fact Linhof)

When I first unscrewed the rear element from the shutter a shim / spacer fell out. It cannot have been mounted correctly as it was sitting between the retaining ring and the rear lens's barrel. It didn't fit there as the diameter of the shim is too large. It looks like it should have been mounted between the board and the retaining ring. (The rear lens's barrel actuates against the retaining ring.)

As I happen to own a micrometer (a nice Japanese one from Mitutoyo) I found out the shim's thickness is around 60 micron (62 micron, i.e., 0.062mm is more accurate, or around 2.5mil for the imperially inclined). That's a pretty fine adjustment, considering that the Sinar lens board that I just mounted the lens on is around 800 micron (0.8 mm or around 31.5mil) thicker than the original Linhof board. Assuming that the shim was appropriate for the Linhof board, adding a shim here seems to be making things worse. More importantly, will this lens not perform properly if I don't have 800micron (or, better, 740 micron to account for the shim) machined away from the Sinar board's mounting area?

Making things worse: I don't know the provenance of this lens. So there is no way to know if it was originally mounted on the Linhof board that it came with. (I don't think it was, because it didn't have a notch to fit the pin on the shutter to lock the lens's orientation on the board.) Or even if it was originally mounted in the Prontor Professional shutter that it came with.

In other words, is there any way of knowing whether the lens was properly spaced on the Linhof board in this shutter, assuming that the shim was appropriate for that combo? What would be needed to verify the correct spacing of this lens?

Or should I simply not worry about this? This here post suggests that for standard and long lenses the spacing is not critical. For modern ultra-wide lenses and digital lenses one apparently should worry as the optics probably require much more precision. This lens is a Rodenstock Grandagon 155mm f/6.8 (non-N version) that I want to use on a 5x7 format. That makes it somewhere on the wide end of normal, but not super-optimized, ultra-wide optics by a long shot. Plus it's an old (1970s?) lens, as it is pre-N. (Don't know when the N version was introduced.) That sounds relatively unsophisticated optically.