Complex sentence: Some outlets selling cuckoo clocks make explicit mention of the fact that all their clocks carry the seal, irrelevant of who the actual manufacturer is, similar to a bottle of Champagne can be called such based on region irrelevant of which orchard produced the wine.
Split into simpler sentences: Some outlets selling cuckoo clocks make explicit mention of the fact that all their clocks carry the seal, irrelevant of who the actual manufacturer is. This could be similar to a bottle of Champagne being called such based on regional manufacture, irrelevant of which orchard produced the wine.