There are four possible explanations.
1. The circuit design of your Wyetech Opal may not be particularly sensitive to variations in tube parameters.
2. While the internal tube design characteristics of the same tube from different manufacturers can vary, it doesn't mean they always do. Your Ken Rad and Philips may have been closer in characteristics than some other combination.
3. There was a difference but it is masked by other aspects of your system.
4. There was a difference but you may not be particularly sensitive to it. Different people listen for different things in music and the change resulting from this tube switch may simply fall in an area that isn't very high on your list of sonic priorities.
It could also be a combination of more than one factor noted above. There are also subcategories (you needed longer burn-in or more listening time/different music in order to hear subtleties, etc.) but you get the idea.
The primary point should be you have tried it for yourself. Even though someone else may have different results from the same experiment is ultimately irrelevant for your situation.
1. The circuit design of your Wyetech Opal may not be particularly sensitive to variations in tube parameters.
2. While the internal tube design characteristics of the same tube from different manufacturers can vary, it doesn't mean they always do. Your Ken Rad and Philips may have been closer in characteristics than some other combination.
3. There was a difference but it is masked by other aspects of your system.
4. There was a difference but you may not be particularly sensitive to it. Different people listen for different things in music and the change resulting from this tube switch may simply fall in an area that isn't very high on your list of sonic priorities.
It could also be a combination of more than one factor noted above. There are also subcategories (you needed longer burn-in or more listening time/different music in order to hear subtleties, etc.) but you get the idea.
The primary point should be you have tried it for yourself. Even though someone else may have different results from the same experiment is ultimately irrelevant for your situation.