Think of a thread holding those little testes. Sometimes it isn't very long and so while they pass through the inguinal ring, as they should, during birth they are high up and slammed against the ring. Sometimes, as the testes mature and get larger, the thread "stretches" for want of a better description and they are now able to be palpated easily. These are the ones that magically appear in the months following birth. If they are external to the ring, it is easy to get them but if they didn't pass through, then you have to find them meaning a larger area of surgery. Breeders have been know to "massage" the groin in hopes of bringing them down. Not sure that it helps any but if you are pretty sure you felt them at one time I can see why one would try. A lot of dogs that do have two descended testicles will suck them up to the ring when manipulated especially if the "strings" are short.
