You'll need to check this, but my limited understanding is that the security industry pension fund collective agreement is a party only agreement. (By coincidence, it came up in discussions with a Trade Unionist a couple of weeks ago).

If I was in your shoes, I'd examine your position very closely before rolling over. When it comes to pension fund contributions, trying to rectify a historical issue like this after the fact comes with a statutory sting in the tail - section 13A late payment interest.