All of that together prompted me to comment,
The qualification of GMs Gulko, Ivanov, and Kudrin, is not consistent between the two sources. GM Ivanov's qualification is confirmed in TWIC 209, but the details about the other two GMs need further investigation.
TWIC 209 reported,
12) Panam Championship in Venezuela GM Alexander Ivanov took the single qualifying place for Las Vegas scoring 6.5/9 ahead of Alexandre Lesiege on 6.
As far as I can tell, this was the first Continental Championship to serve as a qualifier for a World Championship. The same issue of TWIC, 'The Week In Chess 209 - 9th November 1998 by Mark Crowther', also carried news about that year's U.S. Championship.
3) US Championships 1998 In group A Nick DeFirmian and Dmitry Gurevich progressed to the knockout stage and Seirawan, Dzindzichashvili, and Kudrin played off for third place seeing Kudrin qualified for Las Vegas eliminating Seirawan, possibly one of the US's best prospects. There was a four way tie in group B and Gulko, Benjamin, Fedorowicz and Shaked played off seeing first Benjamin qualify after a round robin involving the players, then Shaked beating Gulko to take the other place.
TWIC had no crosstables for the playoffs. The February 1998 issue of Chess Life also gave no details. In GM Nick de Firmian wins the 1998 US Championship! (archive.org -> uschess.org), USchess.org reported,
Standings: Group A after 7 (Top 2 Advance to Semi-Finals); de Firmian and Gurevich Advance; Kudrin takes 3rd in play-offs de Firmian and Gurevich qualify for the two Semi-Final spots from this group and do not need to go through the play-offs. Kudrin wins the play-offs to take third in the section and qualify for the WCT ['World Championship Tournament'].
Standings: Group B after 7 (Top 2 Advance to Semi-Finals) Benjamin and Shaked advance to SemiFinals; Gulko takes 3rd. There was a play-off on Sunday between Gulko, Benjamin, Fedorowicz and Shaked to determine both the two who would advance to the Semi-Finals on Monday and the 3rd place who would also qualify for the 1999 FIDE World Championship Tournament event. Benjamin and Shaked advanced to the SemiFinals; Gulko took 3rd.
Since the U.S., aka Zone 2.1, produced six qualifiers with only five qualifying spots, I'm guessing that there was some sort of arrangement among American chess officials to have both Gulko and Kudrin qualify using a spot reserved for the Las Vegas organizers ('Nominee by the Administrator').
I'll add all of this to the page (C18) Zonals 1998-1999 (m-w.com), under '2.0 San Felipe (VEN) 1998-10' [new] and '2.1 Denver 1998-10'. I'll also add any further info if I discover it.