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OSE crawls a different number of domains/pages with each update. It is normal to see fluctuations in all of these metrics for for links to appear/disappear in OSE reports. OSE and Linkscape data is an extremely valuable for gauging site/page strength, as well as a healthy amount of backlinks to a given page. I do not think it is a great tool to use for benchmarking your site authority or backlink profile growth, due to the inconsistencies between their indexes (or is it indices). If you are tracking competitors with it, you will likely see similar fluctuations in there data as well.