What was the original "Lea & Perrins" recipe from Bengal?

The trouble with the Lea & Perrin's story & Lord Sandys' "original recipe" is that it is mainly myth/fable/advertising copy (I'd hate to outright call it a lie…)

Worcestershire Sauce originally was basically curry powder and water, with anchovy sauce. It didn't start from a Bengali sauce at all, it started from curry powder, which someone decided to mix with water.
The rest is kind of true; it was too strong when freshly-made but after having been abandoned in a cellar for some time, turned out more palatable.

It's never been impossible to copy, though perhaps difficult to get exactly the same. HP Sauce did a similar thing with a thick sauce - they went the fruit route; somebody was thinking of chutneys when they modified to arrive at that. Some companies make both, thick and thin. A million others make generic 'brown sauce' all tasting just about the same.

Interestingly, a later Lord Sandys himself later tried to cash in on the story - http://lordsandys.com/product-info/ though never really gained the worldwide reputation Lea & Perrin managed to solidify.

From the lovely, if rather dated in its HTML skills, Science of Cooking - Worcestershire Sauce

at the date of the legend, "Lord" Sandys was actually a Lady. No identifiable reference to her could possibly appear on a commercial bottled sauce without a serious breach of decorum. It is likely her heir who agreed to sell the recipe.

To abandon the unrevised legend and substitute a more accurate version that was published by Thomas Smith, Successful Advertising, (7th edition, 1885):

we quote the following history of the well-known Worcester Sauce, as given in the World. The label shows it is prepared "from the recipe of a nobleman in the country." The nobleman is Lord Sandys. Many years ago, Mrs. Grey, author of The Gambler's Wife and other novels, was on a visit at Ombersley Court, when Lady Sandys chanced to remark that she wished she could get some very good curry-powder, which elicited from Mrs. Grey that she had in her desk an excellent recipe, which her uncle, Sir Charles, Chief Justice of India, had brought thence, and given her. Lady Sandys said that there were some clever chemists in Worcester, who perhaps might be able to make up the powder. Messrs. Lea and Perrins looked at the recipe, doubted if they could procure all the ingredients, but said they would do their best, and in due time forwarded a packet of the powder. Subsequently the happy thought struck someone in the business that the powder might, in solution, make a good sauce. The profits now amount to thousands of pounds a year.

There's a second confirmation of this being the potentially "true story" at https://www.foodbeast.com/news/worcestershire-sauce-history/

There's also a BBC News story about a potential discovery of the original recipe - Recipes for secret sauce emerge which gives this as the ingredients list, but no detail on how they transformed that into the famous brown stuff…

Sauce ingredients:
water - 20 1/2 lbs
cloves - 2 lbs
salt - 10 lbs
sugar - 34 lbs
soy - 8 gallons
fish - 24 lbs
vinegar - 18 gallons
acetic acid - 2 gallons
essence of lemons - 8 oz
peppers - 5 lbs
tamoraide - 14 lbs
pickles - 40 lbs

I don't think there's really any doubt that Messrs Lea & Perrin took the beginnings of an idea and turned it into something rather spectacular, just that the 'origin story' is perhaps best left to the mists of time.