If there are any miraculous events, I am not aware of them.
Technology, science and society don't exist in vacuum, as you noted, most discoveries are a logical next step. While it's important to distinguish incremental improvements of existing theories or technologies (like steadily raising speed of CPU clocks, or increasing precision of measurement of physical constants) from basic research discovering new phenomena and leading to new technologies (by feeding applied research with those phenomena and ideas), they both work by building on existing foundations. Main difference is, in latter you can't really predict what you will find (that's kind of a point of basic research, to find out), while in former you can make general projections and predictions on rate of improvement and limits.
Most of the science and technology (if not all) would be discovered later by someone else if for some reason historical discoverer wasn't available.
Same works in reverse, many technologies and ideas appeared before their time, and slid into obscurity, because there was no need of them, or there was no axillary tech to make them useful.
Good examples are steam power, mechanical computers and smartphones. While they are examples of ideas or devices failing to catch on prematurely, they show exactly why that happens, and what happens later, when, figuratively speaking, world is ready and time has come for them to catch on.
First steam power dates back to antiquity. It's simple, but shows that work can be extracted. However, without auxiliary knowledge, like knowledge of thermodynamics, it wasn't improved to the point of being useful, furthermore, there wasn't so much need for mechanical power back then. Through most of history, windmills and watermills were sufficient, until advancements in tools led to construction of mechanical looms and lathes, which rapidly increased demand for mechanical energy. At the same time, mechanical tools, allowed for construction of more precise parts, in greater quantity, leading to positive feedback loop of industrialisation.
Antikythera mechanism was a remarkable mechanical astronomical/astrological computer from antiquity. However, it was designed to be more precise than tools and craft of the time could build it. At the same time, there was no computer science, calculus, or even concept of "0". Because of lack of axillary knowledge and technology, whoever designed and built it wasn't able to generalise the device and thus, it remained a very specialised novelty.
Babbage's differential engines were mechanical general computers, designed nearly 100 years before electronic computers. That's the closest to major alternate history that I know. There was no computer science back then and there was little interest in computational power, furthermore, mechanical computers would be large, error prone and less efficient than electronic ones, but that was probably the first time in history where all the elements for computer to become reality were in place. There was steam power to drive them, there was design, tools and alloys might have been up to the task, and there was Ada Lovelace who might have been able to play the role which Alan Turing played nearly century later. However, there was little need for computers. Practical applications of early XX century computers were encryption/decryption and calculating firing solutions or firing solution tables for submarines and artillery, at the time of Babbage, neither of those were advanced enough (or even present) to warrant existence of computer. Thus, Analytical engines were never built, perhaps if there was someone else to the duo of Charles Babbage and Ada Lovelace, someone who could see practical applications the history might have played differently, but as it is, Analytical engine served as the theoretical foundation for further developments.
Smartphones are quite ubiquitous nowadays, but they are not the first attempt at such device. First PDAs appeared in 80s, but without axillary network infrastructure, cheap computational power and plentiful storage, they didn't catch on. Later, with advancements in infrastructure, processing power, batteries, screens, wireless communication and lot more, phones started acquiring new features, effectively merging with PDAs, until finally in mid 00s all was in place to begin the era of smartphone.
Louis Pasteur said that "Fortune favors the prepared mind". Have Alexander Fleming not been bad at keeping sterile conditions, or haven't been knowledgeable enough, someone else would have discovered the penicillin. It already was known that some moulds had antibacterial properties, and research was done in that field. Alexander Fleming certainly wasn't the only capable of that discovery, but chance decided he had greatest opportunity, and he used it to the fullest.
Now, this doesn't mean there aren't discoveries fitting your criteria, but I am not aware of them.
