## Problem 072 — rank:225

**Title:** RNA-velocity identifiability

**Added binding assumptions (LaTeX):**

```latex
Include the latent cell-time sampling law in $P_\theta(U,S)$. Without an external time scale, simultaneous rate rescaling can preserve snapshots while changing velocity magnitude; signs may have separate ambiguities. A sign guarantee requires a stated noise model, expression floor and margin $v_{\min}$. New constrained estimators do not by themselves establish identifiability under arbitrary transcription histories or uncalibrated sampling.
```

**Direct edits:** 0. **Fresh external checks:** SC03, SC04