I agree well with Snipe. It is likely that your original stocker WE are growing slowly especially if they have low relative weights. Note males grow more slowly compared to the females. The 19"er was likely a female and smaller ones are males. Pond walleye usually do not grow much bigger than 4 to maybe 5 lbs at 23-24" maximum. If you grow some 25" consider yourself fortunate and doing something right. Natural reproduction is very rare in regular pond habitats but not unheard of. Do not consider that WE are reproducing in your pond unless you catch some that are 8"-12" long. Do come back and tell us if you catch some 8"-10 walleye from your pond.