The lock on the site of the link was built in 1802 to connect the Stratford canal to the Warwick and Birmingham, lock 21 did not exist then, so the link lock was used to drop the level to that of the W & B. When more money was available to continue the line of the Stratford canal to Stratford in 1812, lock 21 was built and the link lock had its cill removed and guillotine gates installed. The two canals were now on the same level. After complaints by the W & B legal action was taken, and in 1818 the link was filled in and lock 20 built, there was now no longer any risk of losing any water to the Stratford canal. In 1995 the link was re-opened to save boats going from the GU to Stratford using a possible two lock fulls of water, and the reservoir above 20 and 21 running low. I don't think the steamers ever went to Stratford so would not have used lock 21, and since the re-opening of the link, President has never been through this lock. Neil Ratcliffe did once bring them through the link in 2004 but only to wind the boats before going up the GU to Birmingham. Today's lock numbering system is used - notice the difference is the various editions of the popular canal guides.