First of all, I would verify with the store where you got these "jumbo worms" whether they were just large meal worms or another species called "super worms".
That you were able to get them to pupate and eventually arrive at adulthood, makes me suspect they are ordinary darkling beetle meal worms and not super worms.
Second, carrots are better than potatoes because they don't mold, and mold can be deadly to your worms and beetles, causing die-offs and poor development.
Have you heat-treated your wheat bran? Moist substrate conditions can cause grain mite infestations and they can seriously damage pupae, resulting in deformed beetles and dying pupae.
Third, after three months time you should be able to see movement when you disturb the wheat bran around the water source. The new baby worms may be too small to see easily, but they will cause a very noticeable disturbance in the substrate when they are moved with your finger.
Fourth, if you keep your beetles and worms at temps above 75F, you will see much faster development.
