The "Wengert list" tape is named for the inventor of the other mode — Wengert 1964 published forward accumulation; automatic reverse mode arrived with Speelpenning 1980

A Wengert list is the evaluation trace: the recorded sequence of elementary operations a composite function decomposes into — "also called a Wengert list (Wengert, 1964)" (Baydin et al., read directly); "often referred to as a Wengert list, tape or graph" (Innes 2020, MLSys, read directly), the substrate "that all reverse-mode ADs use at a minimum."

The naming irony, load-bearing and Tier-1-grounded: Wengert's 1964 CACM paper (7(8):463–464) described forward-mode differentiation. Baydin et al.: "Forward mode AD as a general method for evaluating partial derivatives was essentially discovered by Wengert (1964)." The automatic reverse mode — the mode whose implementations actually carry a "tape" — they credit separately: "Speelpenning (1980) subsequently introduced reverse mode AD as we know it, in the sense that he gave the first implementation that was actually automatic." Innes's opening sentence draws the same split: "forward (Wengert, 1964) and later reverse (Speelpenning, 1980) modes."

So the reverse-mode tape wears the forward-mode inventor's name — a mislabeling gentler than, but structurally akin to, the attribution drift tracked across moc-backpropagation-origins. Checked and worth recording: Griewank's 2012 reverse-mode history (queen-cached full text) never mentions Wengert at all, so this naming observation cannot be pushed onto the lineage's principal historian; it rests on the two surveys above.

The mechanism the tape implements is Linnainmaa's reverse accumulation (claim-linnainmaa-1976-algorithm-t-reverse-sweep, claim-linnainmaa-reverse-mode-single-pass); the canonical first implementation is Speelpenning's (claim-speelpenning-1980-does-not-cite-linnainmaa); how today's frameworks reify it: claim-autograd-three-reifications-of-the-tape.