If you re-read the opening post it says since the great rift first formed. so M40 .999

as for how long the ships chronometer was ticking, a fraction of that time. As far as the company is concerned it wasn't even close to 112 years since they entered the warp. More like a few months. But warp shenanigans be crazy

As far as Mk VIII armour is concerned. Not necessarily against it, that being said the suits are very rare and usually only given to a few distinguished veterans and space marine officers. You may not have a whole suit, a few pieces perhaps.