I would not consider Wikipedia as a reliable source for info - maybe a general guideline. I've given up on trying to correct all the mistakes on the various Canada Southern and New York Central related pages - including the 1290/1291 page cited. Too many listings are based on assumptions, heresay and non-factual information that have been repeated over and over.
The last steam locomotive to operate on the CASO was 1290 on April 27, 1957 - with an official last photo -
http://www.canadasouthern.com/caso/imag ... 290-38.jpg
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However, there was also a dozen 0-8-0s and 2-8-0s still operating into late April 1957 until delivery of the dozen GP-9 units from GMDD replaced them.