While the blood manipulation after the introduction of the ABP became more technical and sophisticated, the magnitude of the effect is significantly lower as many parameters must be monitored and kept in tandem. Even if we assume that it is possible to elevate hematocrit/hemoglobin by 10-20 % without undetected, just by considering the following anecdotes, it remains significantly lower when compared to what took place in the 1990s:
1) Here is a longish quote from Matt Rendell's Pantani biography about the infamous dblad.wbd - file recovered from the Ferrara laboratory about the hematocrits of cyclists:
In addition to possible different equipment, there is always some natural fluctuation both at the low (hemodilution, anemia) and at the high end of the figures (dehydration), so just contrasting the high vs. the low slightly overestimates the variance, but you get the story. Also according to a chart in the same book, someone of the Ferrara cyclists had his hematocrit at 63 %, reminding me what soigneur Jef D'hondt sais about Bjarne Riis's blood.
2) International Ski Federation (FIS) had collected blood samples from 1989 onwards more or less regularly and the highest conclusively recorded hemoglobin values in the 1990s for men and women were slightly below 200 g/l [hct equivalent 60 %). It is well documented that Italian cross country skier Manuela di Centa has some recorded high hemoglobin values, but at least some sources report that her hemoglobin value was in some tests as high as 220 g/l in the mid-1990s, which is some 40 percent above the upper normal limit for women and the hematocrit equivalent of being staggering 66 %! The Rendell's Pantani biography mentions also in passing a group of biathletes and xc-skiers also having huge hematocrit variations from off- to in-season.
Even when we do not know the baseline figures of the xc-skiers, the elevations should be significantly higher than 10-20 %. And these cases are only the tip of the iceberg, because we don't know what went on in cycling teams or countries of which we have do documentation whatsoever.
I see very little reason not to believe that there was something similar going in the long distance running during that decade. The fact that Ramzi didn't care one iota about his reticulocytes and OFF-scores even when they were monitored just illustrates the point, and I see zero reasons to think that athletes were more conservative in the 1990s when rEPO couldn't be detected and there was nobody in the world who even knew about your high hematocrits as the red precious bodily fluid wasn't even collected by the doping testers or by the researchers.
It is kinda funny that while I don't even agree with Bad Wigins, I do find his chronology quite still surprisingly consistent.