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    $\begingroup$ If I change the initial time of integration to 10 z - 10 to match the time in the initial history, answers are computed. Do the solutions see right? $\endgroup$ Commented Jun 17, 2024 at 20:13
  • $\begingroup$ @MichaelE2 This has solved my problem. Thank you! One thing I am still confused about is that in the documentation for DDEs all of the examples have an initial time of integration that is less than or equal to the longest delay present in the equation. However, it would seem that is not necessary, and even caused errors for me. $\endgroup$ Commented Jun 17, 2024 at 22:28
  • $\begingroup$ You're welcome. I thought I had an answer, but after thinking about it, I'm not sure I understand either. Usually the domain $[a,b]$ as specified by {t, a, b} in NDSolve[] is independent of the DE. It does not even have to include initial or boundary conditions. I think there must be some internal test for the initial history that makes a mistake when it is given by an InterpolatingFunction. See the second method in my answer for a way to trick NDSolve into accepting it. If the solution seems wrong, let me know. $\endgroup$ Commented Jun 18, 2024 at 15:14
  • $\begingroup$ Thanks for the accept. I thought such a well-written question exposing a problem would have attracted more interest. In any case, I'm going to mark it a bug. If the community disagrees, we can open a meta Q&A. You can report the bug to WRI from within Mathematica, menu Help > Give Feedback.... $\endgroup$ Commented Jun 19, 2024 at 15:59