[dginev]

Can confirm. From an ar5iv standpoint, 2.56% articles currently fail to convert entirely, and 22.9% have known errors to the converter. That leaves 74.5% of nominally usable articles. This success rate is noticeably lower for the newest batches of arXiv submissions, as the converter hasn't caught up with the most recent package innovations.

We have a plan in place to meaningfully fall back for unknown packages, but that will take at least another year to put in place, and likely another couple of years to stabilize.

Meanwhile, there is some hope that with arXiv launching the HTML Beta we will get more contributions for package support (LaTeXML is an open source project, with public domain licensing, everybody benefits).

But again the original point is spot on. Coverage will be hit-or-miss for a while longer yet, for an arbitrary arXiv submission. The good news is that authors could work towards better support for their articles, if they wanted to.