A few ordinary reasons, none of them a judgement about the practice:

• It is new, or it moved. We build listings from state licensing records and from practices' own websites, and both take a while to catch up with a practice that opened, moved or changed its name recently.
• The practice has no website we could read. Much of what we show about a clinic — its hours, its services, who works there — we read from the practice's own pages. Without those, there is very little to show.
• We are not sure enough yet. We would rather leave a veterinarian out than put up a page that names the wrong person or the wrong address, so anything we cannot confirm against a source stays unpublished until we can.
• It is here, under another name. Try searching the street, the town, or the veterinarian's surname — a practice is often listed under its registered name rather than the one on the sign.

If you want to help us make this site better, it's easy to suggest missing information, and we'd all appreciate it!