City got fined I recall for missing loads of drug tests in the 100 point season.
Guardiola works with 2 Catalan doctors who are implicated in the " Operation Puerto" case, where Spanish riders, Real and Barca , Spanish national team were implicated where evidence has been sealed by the Spanish state.
City were fined for three violations of the whereabouts rule that allows testers to randomly call players for tests on zero notice. The first was the (admittedly odd) decision to give six reserve teamers a day off which meant they weren't there when the testers came knocking. The second was Pep calling them all in the day after a game for remedial training and a reserve team player not being at home (where City told the testers he would be) as a result and the third was a first teamer being unavailable for a test because City had moved hotels. All of them are bascially admin errors in not updating the whereabouts system at short notice. Cock-up rather than conspiracy.
As to Puerto... The only athletes busted under Puerto were cyclists, however, it was widely speculated that there were footballers, track and field athletes and "A tennis player" implicated in Manuel Fuentes' records... However, it would seem odd if Barca were using a doctor in Madrid who was also providing the same services to Real, given that the reason you dope is to gain an advantage it would seem odd to seek the advantage at the same source as your major rivals especially where sensitive information about blood values would be available to him.
I have no doubt that almost every high-level sport was and is pushing the boundaries of what is legal but I would be extremely surprised if multi billion pound industries like Barca and Real were outsourcing doping on a team-wide scale to a moonlighting Gaenacologist like Fuentes who, by all accounts, was a total loose cannon. The cyclists implicated were paying him out of their own pockets in the order of €2,000 a month plus bonuses. I imagine that those clubs could hire a leading haemotologist to lead their programme... In my view, if their players were clients of Fuentes, they were doing it off their own back.