i have heard on a number of occasions lawyers and judges saying that they cannot, at trial, award retroactive support for the pendency of case if no interim (called pendente lite in New Jersey) support motion was made seeking support.

In the unreported case of Bright v. Bright decided July 9, 2009, the Appellate Division firmly holds to the contrary, affirming the decision of the trial court.  While the case is very fact specific, the logic of the decision was clearly enumerated as follows:

The purpose of pendente lite support is to preserve the status quo, maintaining the parties in the positions they were in prior to the litigation. Mallamo v. Mallamo, 280 N.J. Super. 8, 11-12 (App. Div. 1995); Rose v. Csapo, 359 N.J. Super. 53, 58
(Ch. Div. 2002). "Maintenance of the status quo involves payment of the marital bills and expenses necessary to maintain the dependent spouse at the standard of living enjoyed during the course of the marriage." Rose, supra, 359 N.J. Super. at  60.

Moreover, logically, if someone is not receiving proper support during the pendency of the matter, eatery because they didn’t seek it, by agreement or by court order, why should it matter how the deficiency occurred?