According to spec that tag is used in kind 1. NIP-23 uses kind 30023 and clearly defines expected tags. I'm fine supporting both but other clients might not even show it if it doesn't have a title.
nostr:npub107jk7htfv243u0x5ynn43scq9wrxtaasmrwwa8lfu2ydwag6cx2quqncxg, "subject" is a standardized tag. "title" only shows up in NIP-23. I wonder why "title" was created since we already had "subject".
Discussion
I'll go ahead and code it even as it seems redundant.
I wondered why we had both too. Ideally it would just be title shared for all cases that need a header for an event.
I'm sure it was just an oversight. In my reading most people including myself do not have a complete overview of NIPS (especially as so much of it is in the PR's and issues and not the actual repo). Maybe we should submit a PR to harmonize. IMHO we need to do breaking changes to tidy up nostr spec now before things get so big it becomes impossible.