First of all, there are a lot of RC's that will emulate LSD being loaded onto blotters and sold as LSD.
Then you have variations in strength from hundred milligram plus tabs, through gels, microdots and pills with 300 or so ug to tabs with just tens of ug on.
LSD decays in the presence of chlorine (used to bleach paper at the mill), light and heat. So what might have started out as a good dose can go bad if it's not stored carefully.
There are indeed close analogs of LSD. ALD-52 is one of them, which is potentially even more active than LSD-25 by a tiny amount - although some argue it's slightly less active. Whatever the exact amount, it's real close to LSD-25 - it's meant to be slightly less anxiety inducing, but there's not much the differences. ALD-52 is supposed to have been sold as LSD in a line of pills called 'Orange Sunshine' back in the hippie days - who said misrepresentation was a new thing? It has quite similar effects though, so it's not quite as bad as the random pills of today - where the dirty ones can be annoyingly bad or a serious health risk. The people arrested claimed they couldn't be charged because they were caught with ALD-52, which hadn't been listed for regulation, but the court decided that they deserved some jail time anyway since the only known method for producing ALD-52 was to first make LSD, which was illegal. This was the beginning of analog scheduling in some ways - the court recognized that they were trying to circumnavigate the original law to achieve the same end result.
I've read a lot about purity and different methods, but I think the main defining factor for acid is whether or not the people running the lab know how to setup and run column chromatography with a good separation, how much they decide to dose at and what they absorb it with. The column separation should remove just about everything that a particular method could tint a product with. It's not easy at first, but it's the kind of skill a 19 - 21 year old chemist will have practiced. Modern chemists have HPLC available to them, which is an advanced version of column chromo that can produce some of the most pure samples possible for analytical chemistry - much better than Hoffman himself could have produced. Whether or not your average lab and dealer chain use it or make it last with handling is another thing.