Can my seed phrase have a word count other than 12, 15, 18, 21, or 24?

You restored your wallet with a phrase that doesn't have the number of words you expected, and you're wondering if it's wrong or if you lost your bitcoin.

What counts as a BIP-39 phrase

According to BIP-39 · github.com/bitcoin/bips/blob/master/bip-0039.mediawiki, the standard defines phrases of 12, 15, 18, 21, or 24 words, and no other amount. There is no BIP-39 phrase with a different word count.

If your backup has a different length, it does not comply with BIP-39. That doesn't mean it's invalid: there are other seed standards and formats.

What if my phrase has a different number of words?

It could be that you wrote down too many or too few words, that you're looking at a word list from another system, or that your wallet uses a format other than BIP-39. Don't panic yet.

First, verify how many words your backup has and compare it with what the wallet you're using expects. If it doesn't match, check that wallet's documentation.

What to do when the length doesn't match

If you count and the number is not 12, 15, 18, 21, or 24, your phrase is not BIP-39. Look up which format your original wallet uses; for example, Electrum's seed is not BIP-39 even if it has a different word count.

Do not use the phrase in a different wallet without understanding the format. If the original wallet accepts it, it's probably valid for that system. If it doesn't, you may have a copying error.

Not being BIP-39 doesn't mean your backup is broken

Source: BIP-39 · github.com/bitcoin/bips/blob/master/bip-0039.mediawiki