Adding to my colleagues' posts.
I envisage two different scenarios:
1. Components built by you (and I am not familiar with nuclear reactor configuration) are regulated by provincial laws and you are obligated to comply with the latest edition of the ASME Code. That would be typically the case of pressure envelope. In this case you have to use the latest Code edition regardles if you stamp them with code stamp or not. I strongly advise to talk to Ontario provincial presure equipment authority if you can not establish the scope of their involvement in your product. Also some research of state regulatory bodies of the states where the components are installed should give you enough insight. I found those authorities are very open to cooperation and offer a lot of support.
2. Since the components are not regulated they don't fall under Ontario jurisdiction but require pressure vessel design and ASME Code is used to ensure the design meets integrity requirements. This might be a case of propriatory design. In this case it might not be imperative to use latest code edition. There is a catch though, your designes should ensure that the requirements of the code did not change (e.g. PWHT requirements). Well, it is still advisable to review the latest code edition as minimum.
The purchaser may specify in their purchase order that the latest code edition should be used. I do. Than you don't have much choice anyway.
Having said that, in my opinion use of latest code is justifiable. The Code (I assume Section VIII is used) addresses materials, welding and NDE. Those sections (II, V, IX) are revised regularily to address latest industrial trends and developments in techniques and equipment. I don't think you want to overlook these.
Only in the case of very simple components that do not require PWHT and are "off shelf" items of propriatory design based on ASME 1995 I see no direct need to us the latest edition provided someone confirms no changes to the code sections/paragraphs used. That should be addressed in the manufacturer propriatory design specification.
Putting Human Factor Back in Engineering