'painstakingly-documented' is a compound of 'painstakingly' and 'documented'. 'painstakingly' derives from English 'painstaking' (a combination of 'pain' and 'taking'/'to take pains'), where 'pain' comes from Old French 'peine' (ultimately Latin 'poena') meaning 'sorrow/trouble' or 'effort'. 'documented' originates from Latin 'documentum' (from 'docere' meaning 'to teach' or 'to show').

'painstaking' developed in English from the phrase 'to take pains' (meaning to make great effort) and came into adjectival use in modern English; 'painstakingly' is the adverbial form. 'document' entered English from Latin 'documentum' via Old French 'document' and Middle English to mean a written record; the verb 'to document' and its past participle 'documented' evolved to mean 'to record or provide evidence'.

Initially elements like 'documentum' in Latin meant 'a lesson' or 'example' (something to teach or show). Over time 'document' shifted to mean a written record or official paper and then the verb came to mean 'to record or provide evidence'. 'Painstaking' originally emphasized taking pains (exerting effort); its modern sense focuses on careful, thorough attention—thus 'painstakingly-documented' now conveys carefully produced records.