Pharmokinetics is likely the reason for any perceived differences between LSD, 1P-LSD, and ALD-52. That is to say, even though the latter two molecules seem to be LSD prodrugs (according to D. Nichols, 1P-LSD and ALD-52 are incapable of fitting into the necessary receptors without first being hydrolyzed into LSD), the addition of a propionyl group in the case of 1P-LSD and an acetyl group in the case of ALD-52 affects the molecules' lipid solubility, thus allowing them to cross the blood brain barrier more easily than LSD, changing their accumulation rates in the brain, and causing them to produce slightly different effects -- even though they're ultimately metabolized into LSD before hitting the necessary receptors.
Heroin (aka diacetylmorphine) is perhaps the most easily recognizable example of the effect an acetyl group-induced change in pharmokinetics can induce: Despite the morphine prodrug heroin quickly metabolizing into morphine once it enters the human body, the increased lipid solubility bestowed upon it by the addition of acetyl groups allows it to cross the blood brain barrier with greater efficiency and accumulate in the brain more quickly than morphine does, thus producing a significantly different effect even though diacetylmorphine ultimately becomes morphine before hitting the necessary receptors. [Codeine (aka 3-methylmorphine) is another example of prodrug pharmokinetics, yet in codeine's case, its molecular baggage decreases potency rather than increases it.]
Attaching propionyl and acetyl groups to molecules to facilitate better and deeper penetration into the brain via increased lipid solubility before they're hydrolyzed into their pharmacologically-active metabolites is not unique to psychoactive drugs, and a quick Google search for the terms "acetyl propionyl prodrug" will yield many examples of such groups being used to change drugs' pharmokinetics. [Check out "Hydrolysis in Drug and Prodrug Metabolism" by Bernard Testa and Joachim M. Mayer (2003) for many great explanations and examples of such.]
