I have also wondered about the origin of the ZL&T Peterburough misconception. I've also seen reference to ZL&T being based in Toronto. I can say with absolute certainty that they were based completely in Guelph as I have several company newsletters, and have interviewed several past employees. One gentleman, who started working at ZL&T when he was very young, was actually the President of Textile Industries (the successor to ZL&T) right up until the time that it sold out in the 70s.
The only interests outside of Guelph that I can think of is a spinning plant that he mentioned in Ormstown, Quebec, which was built by Brooks Stevens Jr, the president of ZL&T during the war. He claimed that at the time it was built, it was the most modern spinning plant in North America. It was built sometime after the war, in the 50s, after ZL&T had become Textile Industries, and was operated under the name Zephyr Textiles. I haven't been able to find any primary sources to verify its existence, however.
Hope that helps.