Apple advises that you can buy AppleCare+ if you are within 60 days of the original purchase date (ie when it was first sold by Apple or an Apple Authorised Reseller) of your Apple Watch, including if you did not buy it directly from Apple.
If you are beyond that time period, then I suggest that you contact Apple to ask whether or not they are able to assist you.
I'm afraid that no-one here can tell you what Apple will decide. You are not talking to Apple here - this is a user-based technical support community.
Contact details for the US and UK, for example, are detailed here, at the bottom of the page:
Question: When is it too late to purchase Apple Care plus?