Boundary Transparency Index (BTI) v1.0 Supplementary Note: F5 Uncertainty as a Fuzzy Linguistic Extension Pathway

This supplementary technical note documents a post-validation methodological extension pathway for the Boundary Transparency Index (BTI), focusing on F5 Uncertainty as a candidate fuzzy linguistic extension. BTI remains a six-field ordinal 0-12 reconstructability instrument for evaluating whether decision records preserve the minimum informational content required for post-event accountability, auditability, and contestability. This note does not modify the current BTI scoring scheme and does not introduce a newly validated fuzzy instrument. The purpose of the note is to preserve a bounded methodological insight emerging from IJCIS field-positioning work: among the six BTI dimensions, F5 Uncertainty is the most natural candidate for future fuzzy-system extension because decision-point uncertainty is graded, linguistic, and context-sensitive rather than purely binary or crisp. The validation study motivating this note found that F5 produced the largest DER advantage while also showing the widest rater-calibration difference, suggesting that crisp ordinal scoring is useful but may be less expressive for this dimension than for more document-presence-oriented fields. The proposed extension pathway treats decision-point uncertainty as a possible fuzzy linguistic variable, with future work potentially drawing on two-tuple linguistic representation models, fuzzy aggregation operators, or related fuzzy decision-making methods. The note explicitly limits its claim: no membership functions are fixed, no fuzzy rescoring is reported, and no fuzzy validation study is claimed. This record is intended as a supplementary methodological anchor for future BTI development, especially for computational intelligence, fuzzy systems, multi-criteria decision-making, and decision-support-system research contexts.