When Spanish numerals are used, however (p. 545), we get "bilingual suppletion" (Matras 2012) - i.e., a grammatical rule of one language that seems to require switching into another one:
So à dɔn gɛt tri nacionalidad nà dis wɔl. so 1SG.SBJ PRF get three nationality LOC this world ‘So I have three nationalities in this world.’ [fr03ft 102]
The attributive use of Spanish numerals goes along with the insertion of Spanish head nouns – there is no instance of a mixed combination of a Spanish numeral and a Pichi noun:
Lɛf=àn mek è rich a los quinze años. leave=3SG.OBJ SBJV 3SG.SBJ reach to the.PL fifteen years ‘Leave her, let her reach [the age of] fifteen years.’ [ab03ay 138]
In Spanish, of course, numerals other than 1 select for plural nouns.
Now I would prefer to see a wider range of examples before reaching any firm conclusions, because counters like "years" are inherently more likely to cause borrowing of numeral+noun units. But, as described, this language precisely fits the explanation proposed for bilingual suppletion in Souag & Kherbache (2016), based on Myers-Scotton's Embedded Language Island Hypothesis:
[W]here bilingual suppletion in numeral+noun combinations emerges, it will occur only following borrowed numerals whose noun selectional requirements in the source language differ from those in the recipient language.I was, of course, unaware that Pichi displayed bilingual suppletion when I proposed this generalization, so I take this as corroborating evidence. I would be interested to hear of any further examples.