I was doing some more research on a related issue and came across the following:
Section 125 of the Truth in Lending Act - Right of Rescission as to Certain Transactions
paragraph (e) This section does not apply to -
(1) a residential mortgage transaction as defined in section 103(w);
but I was more interested in:
(4) advances under a preexisting open end credit plan if a security interest has already been retained or acquired and such advances are in accordance with a previously established credit limit for such plan.
Wouldn't this cover the subsequent advances on the purchase money HELOC or am I reading more into this?