1099-Ks are only required to be issued for that 20K level (OR 200 individual payments). However, that's the minimum requirement for Paypal - but Paypal can issue these forms for any level of sales or payments b/c the seller would need to be reporting the income regardless...so, it sounds like Paypal might have gotten a visit or a nudge from the IRS this year, and that this may be a "highlight area" for the IRS to look for abuse in...so if you get one, I'd be amending anything and everything to include it...
From H&R Block
"When is Form 1099-K Issued
Not everybody who uses such a service will receive a Form 1099-K, because technically the form is not required to be issued unless:
The service processed more than $20,00 worth of payments, and
The service processed more than 200 individual payments.
If you do not meet both of those requirements you are not required to be issued a Form 1099-K. That being said, that rule is just when the form is actually required. Many entities that process card payments on behalf of their customers will issue a Form 1099-K when the amount of payments and number of payments are far below this threshold. Some will even issue the form when there is a little as one transaction processed during the year.
IRS Enforcement of Form 1099-K Reporting
When it first debuted in 2011 Form 1099-K was treated as almost a second thought. In fact, there was even a special line on the Form 1040 for amounts from the form that taxpayers were specifically instructed to ignore.
Since then, the IRS has started contacting taxpayers whose gross business income is less than the amount reported on the form."
Massachusetts changed their rule to 1099-K's being required for $600 and up, and one other state may have as well. I have no experience with this, but have seen it reported on other financial forums I read so thought I'd share.