Paper 6 (Silva 2026) introduced BPE Mean Vocabulary Morpheme Length (VMML) as a writing system classifier and showed that the Voynich Manuscript occupies a discriminant zone (VMML = 5.918, 95% CI 5.77-6.05) above all 15 tested alphabetic natural languages. This paper (v2.5) expands to 71 corpora across 40+ languages and reports six extended analyses: (1) Alphabetic ceiling confirmed at 5.76; (2) Tagalog (VMML=5.914) is the sole natural-language entry into the Voynich CI, but BC=0.202 distinguishes it from Voynich (BC=0.361); (3) Romanization inflates VMML by 2.4-5.3 units (methodological confound). Extended analyses: (4) Currier A vs B: delta VMML=+1.27, delta CBMI=+0.16 bits -- two quantifiably distinct writing registers; (5) BC coherent across all 7 manuscript sections (CV=6.7%) -- single writing system confirmed; (6) 3D discriminant (VMML x BC x CBMI): Voynich isolated, nearest natural-language neighbor Irish at distance 0.17; (7) Six named hoax mechanisms (monoalphabetic, Vigenere/barbavara, Vigenere/Italian-Knowles 2026, null insertion, syllabic compression, vocabulary shuffle) each fail all three criteria simultaneously; (8) BC orthogonal to all classical textual metrics (|r| < 0.23 vs entropy, TTR, hapax, Zipf) -- genuinely new structural dimension. All code and six extension scripts publicly available in companion repository. v2.3 (2026-06-08): Section 5.9 added - per-folio Currier A/B reanalysis using the Gaskell and Bowern (2022) canonical corpus (36,361 tokens, min_freq=5 BPE). Cross-boundary mutual information (CBMI) identified as primary discriminant: CBMI_A = 1.97 bits vs CBMI_B = 1.51 bits, Cohen d = -1.01, permutation p less than 0.001 (n = 10,000 shuffles, Bonferroni-corrected). CBMI survives within-quire control (pooled nA=46, nB=33; permutation p = 0.0008; Fisher combined within-quire p = 0.001), ruling out manuscript section as a confound. All three metrics (BC, BPE-ratio, CBMI) show A greater than B direction. Fisher combined full-corpus: chi-squared(6) = 40.66, p less than 0.000002. Section 5.1 corrected: direction is A greater than B on BC and CBMI. Finding is orthogonal to Parisel (2026) vowel-selection model. Conclusion 12 added. v2.4 (2026-06-09): §5.10 added — Currier-preserving null model (n = 200 iterations, size-matched) quantifying each metric's section-discrimination sensitivity independently of dialect. Key result: CBMI is the weakest section discriminant (mean |z| = 1.20 across six sections), confirming that the large CBMI A/B gap (§5.9) is not a section-composition artifact. STTR@100 is the strongest section discriminant (mean |z| = 4.75). Herbal section shows anomalously low vocabulary diversity (STTR z = -13.9); Stars shows anomalously high unique vocabulary (Hapax@500 z = +4.4). Demonstrates two independent organizational layers: CBMI tracks dialect, STTR tracks content domain. Conclusion #13 added. v2.5 (2026-06-10): Corpus expanded from 55 to 71 corpora across 40+ languages. §5.11 adds five medieval European corpora in native script via Universal Dependencies treebanks (Gothic transliteration, Old Church Slavonic, Old East Slavic, Ancient Greek PROIEL and Perseus; VMML 3.54-5.18 — all below alphabetic ceiling of 5.748). §5.12 adds 11 Australian Aboriginal language corpora via BibleNLP/eBible (Pama-Nyungan Western Desert, Ngumpin-Yapa, Arandic; Yolngu; Gunwinyguan; Daly; VMML 6.09-8.00 — predominantly above the Voynich zone). Warlpiri (VMML 5.851) is the sole near-entry on VMML but fails BC (0.233) and CBMI (0.244); 3D normalized distance from Voynich = 0.746 (vs. Irish = 0.200, the nearest neighbor from §5.4). Voynich zone is now charted on both sides: fusional alphabetic below (VMML 3.5-5.75), agglutinative-to-polysynthetic above (VMML 6.0-8.0). Voynich occupies a structural configuration not replicated by any of the 71 corpora tested. To our knowledge, this is the first systematic BPE profiling of Pama-Nyungan languages in the computational linguistics literature. Conclusions #14 and #15 added. v2.6 (2026-06-12): Section 5.10.1 adds a prose-only robustness check for the Section 5.10 Currier-preserving null model. Excluding all label, circular and radial loci (8.7% of tokens), every headline deviation survives essentially unchanged: Herbal STTR z = -13.5, Balneological z = -10.7, Stars Hapax z = +4.3; the sensitivity ranking is unchanged with CBMI last in both conditions. A mean-vs-median distributional note (both summaries rank lexical-diversity metrics first, boundary metrics last) and a coverage note (Astro/Zodiac folios carry no Currier tags and are outside any Currier-preserving design) are added. Erratum: Section 5.10 folio count corrected to 226 parsed / 196 Currier-labeled.