OCI's in Europe can go as long as 20K so it's understandable that European car makers are fussy about 'approvals'. Your Tiguan is out of warranty and Castrol EP 'Gold' is not a run of the mill 5w20 'dino' but rather is an excellent oil by all accounts. I seriously doubt it would do a bit of harm in your VW if changed at reasonable intervals like 7K miles. If you want to be safe run it in summer and use VW 0w20 in winter. I still don't know why Toyotas, Hondas, Fords etc...can run 200K+ on run of the mill 0w20 syns. but VWs are so fussy (if you aren't doing extended OCIs as done in Europe?) Is VW metallurgy so different? The OP asked for opinions and that's mine.