There is only one Sunder in G1. Not to be confused with Sundor. And as you said, the only time Sundor's name was spelt as "Sunder" was in the Aligned continuity which isn't G1. So "Sunder (G1)" refers to the character known as "Sunder" (not Sundor) from the G1 continuity family, not Aligned.

The name Sundor was, of course, originally and officially written as サンドル and is meant to be a play on words between "sun" and "condor." 'Sunder' on the other hand is an English word (English origin!) and is a reference to the Yorkshire Ripper. And "Sunder" would be written as サンダー in Japanese anyway.