@piano2
Here's a cut and paste from an old 2011 Premera policy that I have saved:

Pre-existing condition waiting periods;
There is a 12-month waiting period for pre-existing
conditions. A pre-existing condition is a medical condition
that was diagnosed, or for which care, treatment or advice
was received or recommended in the 12 months prior to
your effective date on your Premera plan. Waiting periods
are waived for children under 19.

Benefit exclusion period;
Benefits for transplant services are subject to a benefit
exclusion period and are not available until you have been
covered under this contract for 12 consecutive months.
Benefit exclusion period means a period during which
specified treatment or services are excluded from coverage
under this plan. The benefit exclusion period begins on your
effective date coverage......(continues)

Older plans were even worse. Tough luck if your old insurance company canceled you. Put off Cancer treatment for year? Good Luck with that.