Perhaps useful
Metod, the filter is there to help keep focus on your prints. UV and Infrared light focus at different distances from visible light. Actually, there is a gradient all across the visible light spectrum. Photographic papers are primarily sensitive to the blue and green areas of the spectrum. VC papers rely on this sensitivity by combining two layers of differing contrast, each sensitive to one of these wavelengths. By modifying the amount of blue or green reaching the paper through the subtractive process, a contrast is arrived at.
There are several things that add more UV focus shift to a VC print. Keep in mind that this shift can amount to over an inch in adjustment difference in some cases. First is the use of quartz halogen lighting. This is more of a culprit than tungsten or cold lights. Second is the amount of magenta filtration used to achieve contrast. The higher number filters or settings are usually the problem. The third factor is the lens. Different lens groups and coatings will handle UV quite differently. And then of course there is the paper.
If an enlarger does not have one, most can be gotten as an add-on, or a Kodak Wratten 2E filter can be inserted. Replace the filter every year or two depending on your printing load because it will fade and be ineffective. This problem does not seem to affect fixed grade papers to the degree it does VC.
Unless your filter is obviously warped, discolored, or damaged, there should be no issue. Simple warping of a plastic intermediate filter will not affect UV filtration, but it might "waffle" the light reaching the negative. Project a focused light circle on the board without a negative in place to check for this.
