Yes, vocab drift matters a lot. Most of the pipeline is basically compressing out any of the weird vocab/language stuff, so it doesn't have numbers and proper nouns and is in a sufficiently abstract concept space to cluster nicely. We use a density-based clustering method (HDBSCAN) which when you set min_samples=1 works as an online clustering (i.e., incrementally adding new things is the same as if you re-ran the clustering in batch mode).
It cost ballpark $250k