BCRP (Peru Central Bank) website and December 2001 is used as the start date because that's what the BCRP uses to begin its indexing. What we see is that although the mass wisdom (aka hypnosis) of the PEN getting stronger is true, it's only really true against the US dollar. The multilateral basket of currencies that the Peru Cenbank dudettes and dudes use to measure performance has come back with a clear UNCH result after all this decade is done.
So Peru's Sol is stronger? Nope, it's the US Dollar that's weaker. But you hardly need to go visit Peru to know that one, do you? Peru's Sol is just your actual straight-down-the-middle average perfoming currency, nothing else.