There's a difference between a rollover and a trustee-to-trustee transfer. A rollover is when you take money out of one HSA and you have the money in your hands. Then you deposit that money into a different HSA within 60 days from when you took it out of the first account.
In a trustee-to-trustee transfer you never touch the money yourself. The trustee of one HSA transfers it directly to the trustee of another HSA. Technically this is not a rollover.
You can do only one rollover in any one-year period. But you can do as many trustee-to-trustee transfers as you like.
The following is from IRS Publication 969.
"If you instruct the trustee of your HSA to transfer funds directly to the trustee of another of your HSAs, the transfer isn't considered a rollover. There is no limit on the number of these transfers."
