Monitor 5B and 5jr+ Passive radiator rubber surround

Hi all, as you know I have been refurbishing my 2 speaker set. I have noticed that the passive radiator rubber surround varies between the two speakers. The 5jr+ has a much softer and thinner rubber than the 5B which appears to be s bit stiffer.

Anyone compared the two and noticed this? I was wondering if the one of the std got the rubbers replaced at some point.

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