Reticulation is is caused by the uneven swelling and shrinking of gelatin pretty much constrained by its attachment to the plate. In addition to the physical appearance of wrinkles, silver grains can migrate from the valleys to the ridges, increasing the visual perception of texture or 'grain'.

Frilling starts from the same causes as reticulation, but at the edges of the plate, where water can get under the emulsion and cause waves of swelled gelatin that separate from the glass. Big temperature swings is the major cause of both reticulation and frilling, but in addition, going from a strongly alkali developer to a really strong acid stop bath can do the same thing. The major cause of serious frilling, even if all the temps and pHs are balanced, is rough handling of the plates during processing. Try not to touch the edges any more than absolutely necessary and be as gentle as possible. Also, I remember reading a caution about too-warm hands. I always wear nitrile gloves and work at 65-68F, so I've never noticed a problem with that, but it makes sense. But, all in all, as you've noticed, gelatin emulsion is pretty amazingly tough stuff. You have to really abuse it to have significant problems.