Hi,
You need to get a fibre and do a float test, if it floats then the face fibre is polyprop. This is the most common fibre used to construct Belgian wiltons.
You need to lift the carpet up in one corner, look at the weft shots, do they run in both directions crossing each other, if so it is likely to be belgian wilton.
Most belgian wiltons are patterned.
You are lucky to have gone 5 years without a shrinkage if you are not carrying out the basic tests prior to cleaning, it can save you a lot of time and money.

Mark