Here I don't think the exclusion of Shipulin and Ustiugov is not to do with anti-doping breaches but because for once, the onus is reversed, because of the unusual situation here. I don't know so much about the XC case, but looking at the other biathletes who've been excluded along with Shipulin, that is Volkov and Garanichev, they are the only other members of the Russian Olympic pre-selection who also competed in Sochi - Yurlova was off the team at that point and the other women hadn't broken through yet, whereas the men's team has been more stable, yet Babikov and Eliseev had yet to break through at the time of Sochi, and Tsvetkov missed much of that season injured. The data in the McLaren report did not suggest anything was wrong with the samples that were provided by those three athletes who have not passed the screening per se, however it was an incomplete picture because some of the samples were either missing, had been improperly stored or test results had not been recorded.
This meant there was nothing that could genuinely convey an ADRV, and hence why those athletes have been able to continue to compete unhindered (as Besseberg said this time last year, 22 of the 31 athletes in the report had at that point either been cleared as there was no evidence of wrongdoing on the part of the athlete, or had already served the suspension for the period in question). However, the Russians are not representing Russia per se at Pyeongchang, instead they are in effect representing the IOC via the neutral Olympic Athletes from Russia designation, so are competing essentially by invitation of the IOC only; as such, rather than the onus being on the anti-doping authorities to prove the athlete had been involved in doping, the onus is on the athletes to prove they had not - which is fine for the athletes who weren't in Sochi but for those who were, unless those missing tests or test results could be found, they were going to be in a bad position when it came to establishing that they were not just "not guilty" but "expressly innocent".
Of course, the interesting thing will be to see if Timofey Lapshin lines up when the Games begin. He did not go to Sochi, but was part of the 2013-14 World Cup squad, and he is named in the McLaren report and with a failed test no less. He's served no sanction and is happily racing away representing South Korea at the moment...