I occasionally see discussions where people are talking about using modules from one edition of D&D with another, and suggestions for conversion. One thing that often comes up, especially when people talk about using Moldvay/Cook or OD&D with AD&D is that clerics don't get a spell at 1st level, and hit die are lower compared to AD&D.
All these things are true. However, take a look at how things changed in OD&D as the supplements were added. Monsters became more challenging, for starters. As a result, no spells at first level becomes a "problem" since monsters can inflict more damage each round and might have more than one attack. Changes were made in aspects of the system, and not necessarily followed through in other aspects of the system right away in predicting what the repercussions might be.
The point I'd like to make is that for some changes, not all mind you, but some, like whether a character has a spell at 1st level or whether on average a character will have 1 or 2 fewer hit points each level, or whether ability bonuses give a few more hit points or damage bonuses...etc. etc. etc....leave the burden on the player, not the referee or module, to cope (which is a good thing). When people comment about the power level of modules based on edition, they are often making the assumption that the module was scaled somehow to account for all this, when in fact, for example, differences in the HD and damage inflicted by monsters from Moldvay/Cook versus AD&D are little different. It's true that fewer hit points and less healing capability can make things tougher, but that only means that the players must play according to the situation. This means they might have to flee more often, or stop to rest more often, or head back to town a little sooner to recoup.
We have to keep in mind that no edition of D&D is really a fine oiled machine. There is a lot of variation across and within editions, and it isn't always consistent. Old-school gaming is, among other things, about thinking on your feet and playing smart. You play with the tools at your disposal. The burden is on the player to survive under various circumstances. Don't expect perfect balance, because D&D, at least earlier versions, were not about balance. Things were intentionally designed to not balance in favor of the PCs! You take the tools at your disposal and run with them.