Is there any reason to suspect the nuts and bolts as being less than a normal proper standard specification for nuts and bolts generally? Are the parts sites offering genuine Volvo parts? You could end up removing proper original nuts and bolts, to isntall hopefully equally adequate third party nuts and bolts.
I would tighten up all the nuts and bolts and check them occasionally. If time gives cause for further concern, or if you have become worried and want additional peace of mind, then I would check the Volvo dealer's price for replacement nuts and bolts.
I suspec guess &c. that the usual cause of loose nuts and bolts is inadequate tightening ... or excess vibration ... which I suppose can perhaps most often be a chicken and egg situation. Tighten them up and check them ocasionally.
