echoes, good post.
For a good hint at the use of EPO in the Netherlands in 88, check this post on Van Gennep:
viewtopic.php?p=1906774#p1906774
That said, I totally agree with your assessment that wrt epo in 88 in the Netherlands/Belgium there is a burden of evidence which has not yet been met satisfactorily.
Imo the case of Greg Lemond is (much) different, however, in as far as there are serious rumors about him introducing EPO, including a 1990 whistleblower article. In other words: there is already a reasonable suspicion (beyond his performances). Then if you go look at the available data, it all points in the direction that those rumors aren't just random smoke.
The assumption that he took EPO just answers so many questions and is supported by so much contextual data (do ask if you want me to expand).
For me it's occam's razor.
The only question for me personally is when he got onto the EPO program.
1986 doesn't seem out of reach (see articles linked above, suggesting it was circulating in the States already in that year). It's also the year that Lemond keeps referring to as his strongest year ever.
1987: in the hospital, quite likely (see Sidebar thread for recent discussion)
1988: no idea what happened there.
1989 Giro and beyond: very likely.