Unless I'm missing something, I don't see what exactly links the Bray-produced Jerry on the Job cartoons with the earliest Terry Fables. A very slight stylistic similarity in one visual element, between both series of films, doesn't suggest that one artist or company was designing or supplying title cards or intertitles to multiple animation studios. There's little or no deductive reasoning in that kind of assumption/conclusion.
Think about it this way. Animated cartoons are made by animators, cartoonists, illustrators, and so forth. In other words, a team people who could...draw, and arguably also hand-letter text. What point would there be in going outside of one studio's own personnel, who are already doing whatever you need them to do for an hourly salary, and paying someone else on the outside to do something that one of your own guys can cook up really easily?
The original question or assumption, and some of the follow up responses, just don't add up to me. Unless I'm missing something—help me out!
Also, Leon Schlesinger was a businessman. His company, Pacific Title and Art, was in the business of supplying title cards for motion picture productions. This does not mean that he himself was a designer. He simply employed artists who designed and lettered the cards, so he could turn out a finish product for a client. Different business, but same structure as being an animation producer while not being an animator or director himself.
It's a little concerning to see folks jumping to other kinds of conclusions, only based on hearsay or simple misinterpretations in an internet forum...