@GoombaGeek: Not quoting your post.
Did people actually do anything remotely like that in the 1400's? Because, in theory, an Australopithecine could have made stone knives (even with ground edges!) worked wood or something into a circle, punched out the middle, used a stock for an axle, make four wheels and two axles, laid some more sticks down on that, bound it all with sinew or vines or something, and had a cart long before any existed.
But it didn't happen, so having an Australopithecus using such a cart would be an anachronism.
I think the point he's trying to make is that such things were possible in the 1400s. Did people do such things? No, because of the dark ages. I would bet that if there wasn't a period of time where the people in charge were actively destroying knowledge itself, in all corners of the world, then having alkali metals and aluminum would not be out of the question.
I doubt it.
I highly doubt that your claims are anything but exaggeration. The Renaissance started in the 14th century, a century or two before the 1400's cutoff; surely anything that would let those 1400'sers get alkali metals would have let them do so after a century or more of Renaissance or else would have been known before that time where "the people in charge were actively destroying knowledge itself, in all corners of the world." And the cutoff isn't the 1400's in a world with no Dark Ages, it's the 1400's in our world. So, no dice there.
I would just like to point out that you are wrong. The start and spread of the Renaissance dates usually start around the collapse of the Byzantines, in 1453 AD. Most of the scientific, military and cultural advancements the renaissance was known for did not start until around the mid 1400s.
Other dates that are pretty important that 'just' pass the cutoff line: Battle of Agincourt is fought, with massed archer formations forbidden city is built in China (1420); Joan d'Arc is executed for heresy and treason (1431); Incan empire is formed (1438); the 100 year war ends (1453) printing press is made, make the spread of writing easier (1457, Gutenberg Bible; 1490, Torah); war of the roses ends and England is unified (1485); star-forts start becoming built en-masse (1486) and Charles VIII develops 'modern' siege train techniques and the first mobile siege weapon (1498), making sieges possible within days instead of years against the current forts in existence; 'Late' middle ages ends with the new world being discovered (1492), Venice and the Ottoman as hegemonies (~1500), England unified under the Tudors and so forth. THEN the renaissance starts.
You also miss a whole bunch of artists, scientists, philosophers, explorers, political reform, economic reform, religious reform, military reform, tactics, strategy, military leaders and nation states rise to power, all within 1453-1509AD. Leonardo da Vinci, Niccolò Machiavelli, Nicolaus Copernicus, Michelangelo were all born around 1470. Without them, there would of been no renaissance.
As a further note, the 1400 cutoff limit is to prevent steam punk and magitek from entering the game, even though gunpowder, cannons, and petards are already in heavy use before this time. Think of the 1400s as an 'atmospheric cutoff' as opposed to a hard technology limit. So, a compound bow (1966 AD) could easily have been made in the 1400s, but no one thought up the idea because of the gun being made more effective in between those times. Likewise, steam ducks such as the ones in the bathhouses of Rome (~300 AD) may have been around, but they may not fit into the style of DF.