Thanks for your feedback hueyracer.
Indeed FCL.510.H ATPL(H) — Prerequisites, experience and crediting does state that applicants for an ATPL(H) shall (a) hold a CPL(H) and a multi-pilot helicopter type rating and have received instruction in MCC, however (d) states the experience required in (b) shall be completed before the skill test for the ATPL(H) is taken.
Therefore all the aeronautical experience listed under (b) must be obtained prior to the skill test, which logically implies that one must have held a MP helicopter type rating in order to build the 350 hours required prior to the skill test.
Following your rational, one would have to necessarily hold two MP helicopter type ratings in case the skill test is conducted following an initial pilot course. In other words, you are suggesting that it is virtually impossible to undertake an ATPL(H) skill test upon completion of an initial pilot type rating, unless you hold at the time a MP helicopter type rating on the license.
Why wouldn't AMC1 FCL.520.H specify that it refers to an "additional" MP helicopter type rating?
Again, if I understand you correctly, in case you are undergoing an initial pilot course, the only way you can do the ATPL(H) skill test at the end of your course is provided your CPL(H) already holds a MP helicopter type rating?