Part I

Yes, historical IPA that was actually shipped to India was different than modern IPAs in nearly every way. Breweries often massively exaggerate how little their recipes have changed but if you have access to brewery archives you can see CONSTANT tinkering with recipes that, compounded by decades means that beer today is massively, massively, MASSIVELY different than what you'd get in the past despite it being called the same thing.

Let's break down how IPAs have changed by looking at the different elements of beer making.

Barley

First off there's malt which is made out of barley. The kind of barley used by brewers today is not the same as the kind of barley used to make historical IPAs. Plant breeders are constantly trying to develop new strains of grain that have higher yields, more disease resistant, doesn’t have bits of grain falling off the plant before it’s ready for harvesting, etc. How the grain actually tastes is often not the main concern.

A lot of the barley used for historical IPA would’ve been Chevallier barley which has been out of common use for a long time now and which has only recently been revived in a limited fashion: zythophile.co.uk/2013/04/15/revival-of-ancient-barley-variety-thrills-fans-of-old-beer-styles

How much different strains of barley impacts the taste of an IPA is fairly limited but the fundamental base of beer used in IPAs today is different than those in the past.

Malting

After you grow barley, you have to malt it to start to process of breaking down grain starches into simpler carbohydrates that yeast can actually eat. Part of this process is roasting the malt, which is important to dry out the malt as it’ll otherwise rot very quickly. Of course, how long and at what temperature you roast the malt has a massive impact on a beer’s flavor.

Historically when making a beer people just used all of the same malt. What was called “white malt” (because it was roasted very gently so kept a pale color) was the most expensive because it was technically difficult to get everything evenly roasted and dried out without toasting the grain a darker color. But in the early 19th century brewers figured out that more heavily roasted malts were harder to ferment so, despite being more expensive, you could actually get more alcohol for your money by using white malt instead of the amber or brown malt used to make darker beers.

This left brewers in a bind since some of their customers wanted darker beers but they could get people drunk cheaper by using lighter malt. The solution they hit upon was to burn a small portion of the malt so black (this black malt is often called “patent malt” since Daniel Wheeler got a patent for its production) that using only a tiny bit of it would be enough to turn the beer black. After this, brewers would use a mix of different colors of malt to get darker beer.

What does all of this have to do with IPAs? Well historical IPAs were pretty much all white malt which is slightly lighter than most of the malt used for modern IPAs. The closest commercial modern equivalent is pilsner malt but even that isn’t quite the same. Also after brewers got in the habit of using a mix of different malts for darker beers, they eventually started doing the same for lighter beers. Modern IPAs sometimes have a little Munich malt (the kind used to make Marzen/Octoberfest beer), very often have crystal malt (a kind of caramelized malt), and in some cases a touch of biscuit or similar malt (a kind of brown malt that’s roasted too much to ferment much but not anywhere near enough to make a beer brown) to give it a bit of color and flavor in addition to the pale malt which accounts for the bulk of the grain used and nearly all the alcohol. For example, Sierra Nevada calls for 93% pale malt and 7% crystal 60 malt (60 is a measure of how dark this caramelized malt is). Historical IPAs would have used zero caramelized malt which makes a big difference in color and flavor.

After you get your malt, you have to mash it (soak it in how water to get the enzymes to break down the starches in the grain) and mashing techniques have changed over time. The specifics of how you mash mostly effects efficiency (how much maltose you can get out of a given amount of grain) and can make the beer taste thicker or thinner but generally doesn’t have a huge impact on taste despite the specifics of how beer is mashed having changed a lot since the 19th century to become more efficient.

Strength

The average modern American IPA has a strength of round about 6.5%. This is roughly the same as historical IPA that was shipped to India, although the strength did bounce around a lot in response to demand, grain prices, changes in taxation, etc. It’s important to note that while IPAs are comparatively strong beers today, they weren’t in the 19th century when average beer strength was often quite high. The average strength of British beer dropped a lot thanks to grain shortages in the world wars and post-war austerity and has never really recovered from that.