In his book Lützen (2018) Peter Wilson lists the Yellow (Guards) Brigade as having a strength of 1221 men in 17 companies. This is further detailed in André Schürger, The archaeology of the Battle of Lützen: an examination of 17th century military material culture, (PhD thesis 2015) listing the Yellow Guard Regiment of 16 companies (610m, 324p, 192offs) accompanied by the Royal Lifeguard (45m, 38p, 12offs) for a similar total of 1221 men in 17 companies.
And so then on to flags. The Royal Lifeguard flag is illustrated on the cover, Plate F, and page 45 of Richard Brzezinski, The Army of Gustavus Adolphus 1: Infantry (1991). Plate D5 also illustrates two flags from the Yellow Regiment, but these might be post-Lützen replacements.
The flag you have posted is a problem. The small flag on the right of your illustration is from Mark Allen, "Building a Wargames Army for the Thirty Years War, Part 3", Wargames Illustrated, No. 82 (July 1994), pp.42-46. The article includes illustrations of 9 flags attributed to the Yellow Regiment.
However, some time later in Wargames Illustrated, No. 101 (February 1996) the author published Part 5 of his series. He wrote:
"I last looked at the organization, dress and flags of the Swedish army in issue 82 (July 94) of Wargames Illustrated. Since then an enormous amount of new information has come into my possession which has provided the bulk of this article.
This information has been researched and very generously provided by Lars-Eric Hogland of Karlstad in Sweden, and it would be true to say that this article is simply a development of this material into a publishable form.
Lars-Eric first wrote to me after WI 82 to inform me of a rather large error I and made in my assumption about Swedish flags. The problem was that I had relied on a source, much used and repeated by other scholars, which was completely erroneous. The so called ‘Strasbourg Suite' consisted of a number of watercolour copies by a zinnfiguren manufacturer and collector, K. A, Wilke, said to have been taken from an earlier manuscript by an artist called Andersson. Modern opinion in Sweden appears to be that Wilke invented Andersson – and the flag designs – to help sell his toy soldiers and that a number of his pictures were fakes! The problem is compounded by the authenticity of many of Wilke's pictures of Imperial colours and indeed research may later prove that some of his Swedish illustrations are correct. However, for the moment it is better to err on the side of cation and dismiss any Wilke's ‘Swedish' colours that do not have any supporting evidence.
I have the less than pleasant task, therefore, of providing a ‘critique' of my own article and plates, based on Lars-Eric Hogland's first letter."
The Wilke flags dismissed as incorrect are unfortunately the 9 flags attributed to the Yellow Regiment in Allen's WI 82 article. But Allen then goes on to present 7 Yellow Regiment flags taken from an engraving of the 1631 Battle of Werben. He also illustrates another flag attributed to the Yellow Regiment at Augsburg in 1632 as well as the two Yellow Regiment flags that may be later replacement flags. These two flags are also illustrated in Brzezinski's book.
I have been unable to attach a scan of the flags that then may have been carried by the Yellow Regiment at the Battle of Lützen in 1632. But if you e-mail me at ritoewsATmts.net I'll be happy send you the image.