Bernd,
* Mystery how the side plate had all its rust blue removed. Maybe the previous owner tried to use Naval Jelly to remove the pitted side plate's rust and got all the original rust blue finish off as well. Oh well!!
quote: Do you think that I hurt the value any by using cold blue on the side latch?
* I see where your main question has been left unanswered. Suspect this is because there is no "right" answer. At the risk of starting a firestorm, let me crawl out on a limb and hazard a shot at some considerations.
* Cold blue has a distinct smell which will cast a suspicious aura over the entire pistol's finish and originality. To a hard line collector, this will devalue the pistol significantly. Some will say it relegates this pistol to a "shooter" valued @ 50% of a collector's price. Pretty harsh for this example; but, reality.
* Your pistol's condition presents a dilemma. It can not be restored to
original condition. Yet, in spite of the freckling/corrosion spots, the pistol is not in as poor of a condition as initially described. It is a piece of history. Even with the damaged finished(finish loss) on the sideplate, this pistol will command more collector's value in its un-cold blue state than with a "prettier" cold blue sideplate enhancement. I agree with Rich & lugerlou's assessments.
* That being said, it is difficult to accept a white sideplate on an otherwise fairly nice historical example. One alternative would be to ship the pistol to a professional restoration artist, like Thor. The aim would be to have him remove the sideplate's cold blue and re-rust blue the sideplate's finish to match the existing rust blue of the pistol(warts & all). The dilemma is the pistol will now look prettier; but, be partially re-finished. A re-finished pistol may suffer in devaluation as dramatically as a cold blued one.
* Assuming Thor's "re-work", the ethical course, when & if you elect to sell this piece, would be to fully disclose the sideplate's refinish. A price adjustment down from the equivalent collector's value should be expected.
* However, IMHO, this downward adjustment should not be as severe as a 50% shooter's devaluation. The discount would be from a value of an all original blue example and may almost equate to what the price of this piece with an all white sideplate, original finish might bring. Depends on the Buyer/Seller at that pivotal moment of agreement. There is Thor's cost to add to the original investment cost having to be balanced by the sale price.
* In fairness to generations to follow, Thor will place his unique "signature" mark on the area of re-finish with the agreement of the owner. In this case the inside of the sideplate would be a likely location.
* This is your pistol; hence, your decision. Unfortunately, I can't hazard a guess on what the final numbers would be. Possibly other with experience in the re-sale of re-finished pieces can comment on what their realized actuals were as a guide. Also, this degree of devaluation is only one major factor of the decision of what to do.
* Trust this provides some illumination for your question. It is but only one of many opionions I'm sure.