In terms of publication, your goal should be to take your field beyond its present state of knowledge. So, if the sources you are working with are "better" than what has been used before, then you need to convince your reviewers that analyzing them does indeed make a contribution. And you can always list the need to develop a more comprehensive corpus when you discuss the limitations of your study.

Thank you David L Morgan !

I agree and do believe the choice is justified on account of it's potential contribution. We will defiantly put emphasis on explaining that aspect in our discussion.

I was hoping to find studies that made a similar choice, so I can reinforce the claim and establish such a rational, while also gaining better understanding of the implications, but it was quite complicated. I'm assuming this practice tends to happen once in a while when there is no existing corpus, but I was having trouble finding relevant studies since the method is usually not mentioned in the title.

Perhaps a useful methodology or approach could be found by looking into research on religious experiences, such as an analogue. For instance many mystical experiences are similar but written by authors of various religions or belief systems.

For instance any attempt to research into the philokalia-a corpus/collection of orthodox wisdom/spiritual writings by writers of different persuasions, writing about some basic practice of spirituality.