the consensus actually seems to be that the asian guavas (which are cultivated mexican versions that were brought to asia, presumably by spaniards, and not endemic to asia) have less c per g, even if they have more in one of their larger fruits, over all.

see:

Although vitamin C contents were not measured in this work, previous studies where guava germplasm from Calvillo has been included show that Mexican germplasm has up to 520 mg/100 g of mesocarp, compared to 80 mg of vitamin C/100 g of mesocarp in foreign germplasm (Laksminarayana and Moreno, 1978). 

https://www.researchgate.net/profile/Sanjuana_Hernandez-Delgado/publication/231996696_Morphological_and_genetic_diversity_of_Mexican_guava_germplasm/links/0046353a0c34d20aef000000.pdf

& this study which lowballs the asian varieties:

https://www.researchgate.net/publication/318113147_Characterization_of_guava_Psidium_guajava_germplasm_based_on_leaf_and_fruit_parameters

this is leading me to conclude that the "common guava" is probably an american variety, after all, and that i'm not doing poorly by using it as a baseline, given that all fruit has some variation.

ok.

done.