Well, slightly different focus, but you are right.
In a year, TB Magus would probably disappear (assuming TB is a valid theory). However, would his appearance in whatever time period he traveled to be preserved by TTI?
It is an interesting possibility. While creating an army of Robos wouldn't work in the long term, it would certainly work in the short term as long as each new Robo traveled through time on its own volition. That is, original Robo waits 400 years and is picked up by Crono and Co, but TB Robo waits 399 and takes the gate in Leene Square, and TBB Robo waits 398 year, takes the gate, etc. Which, of course, works on the assumption that Time Error doesn't progress apace normal time. Each Robo's a TB, and each would disappear in a year, but for that year one could amass an army, just so long as each TB Robo waits a little less time before traveling through a gate.