another point that I think is important to understand is that Srila Prabhupada was speaking directly to disciples who had been initiated with the bhakti-lata bija.
so, for them, yes the seed of the spiritual body is already there.

But, I don't think you can apply what Srila Prabhupada said or wrote to his initiated disciples to every Tom, Dick and Hairy jiva in the material world.

Sure, for devotees who have been initiated, the spiritual body has already been acquired in a seed form in terms of the particular brand of bhakti they have imbibed from the Guru, Mahaprabhu and the Rupanuga sampradaya.

So, for Prabhupada to tell a disciple "your spiritual body is already there" is not very impracticle because in fact the spiritual body is acquired in seed form at the time of diksha.

The seed of the spiritual body must be fully realized in course of perfection of devotional service beyond the modes of material nature.