Here is an extract from the introduction to the definitive book/catalogue on these issues published by Michael Sagar. More information may be found at the website for Conestoga Press Cachets : ‘In the mid-1980’s, the Conestoga Press, a small print shop in Thornbury, Ontario headed by Justus (Gus) Knierim (who happens to be a stamp collector) was approached by his local post office about designing and producing a cachet to honour the centennial of the Thornbury post office. (...) these products were intended to be sold over the counter to customers for use on their normal mail. Based on the success of this initial venture, over the next 20 years Gus designed and printed cachets on a range of prepaid envelopes and post cards, mostly for sale in post offices in 4 Ontario counties, and also for private users stretching from BC to PEI. The cachets produced were not entirely traditional private productions, in that the Canada Post Office approved the cachet designs, and they were sold as postal products. (...) Gus continued to produce these cachets until 2004. Conestoga Press ceased operations in 2006.’