Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…putative NECs in the orobranchial epithelium, were also unlabeled in Tg(crestin: creERT2);Tg(-3.5ubi:loxP-GFP-loxP-mCherry) (Mosimann et al., 2011; Kaufman et al., 2016) larvae/ metamorphic juveniles, even when nearby neural crest-derived cells in branchial arch cartilages and/ or gill filament…
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